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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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38 ** $QT_END_LICENSE$ |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \page qt-embeddedLinux-opengl.html |
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44 |
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45 \title Qt for Embedded Linux and OpenGL |
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46 |
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47 \ingroup qt-embedded-linux |
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48 |
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49 \input platforms/emb-opengl.qdocinc |
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50 |
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51 \section1 Using OpenGL with Qt for Embedded Linux |
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52 Qt for Embedded Linux provides support for integrating OpenGL ES for |
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53 drawing into a QGLWidget. The current implementation supports OpenGL and 2D |
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54 painting within a QGLWidget. Using OpenGL to accelerate regular widgets and |
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55 compositing top-level windows with OpenGL are not currently supported. |
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56 |
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57 \note OpenGL rendering only works with QGLWidget under QWS. Regular |
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58 widgets cannot currently support it. |
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59 |
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60 \section2 Configure |
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61 |
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62 It is recommended that Qt for Embedded Linux is configured with the |
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63 \c{-DQT_QWS_CLIENTBLIT} and \c{-DQT_NO_QWS_CURSOR} options for optimum |
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64 performance. OpenGL is rendered direct to the screen and these options |
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65 prevent Qt for Embedded Linux from trying to do its own non-OpenGL |
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66 compositing on the QGLWidget contents. |
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67 |
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68 \section2 Using OpenGL to Implement Window Compositing and Effects |
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69 |
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70 Compositing effects can be simulated by adjusting the opacity and other |
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71 parameters of the items within a QGraphicsView canvas on a QGLWidget |
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72 viewport. |
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73 |
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74 While Qt for Embedded Linux does include a complete windowing system, |
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75 using OpenGL to composite regular window surfaces can be quite difficult. |
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76 Most of Qt for Embedded Linux assumes that the window surface is a plain |
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77 raster memory buffer, with QGLWidget being the sole exception. |
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78 The need to constantly re-upload the raster memory buffers into OpenGL |
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79 textures for compositing can have a significant impact on performance, |
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80 which is why we do not recommend implementing that form of compositing. |
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81 We intend to address this problem in future versions of Qt. |
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82 |
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83 \section1 Integrating OpenGL/ES into Qt for Embedded Linux |
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84 \section2 Reference Integration |
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85 The reference integration for OpenGL into Qt for Embedded Linux is for the |
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86 PowerVR chipset from \l{http://www.imgtec.com/}{Imagination Technologies}. |
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87 It consists of two components: \c{pvreglscreen}, which provides the Qt for |
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88 Embedded Linux screen driver, and \c{QWSWSEGL}, which implements a plug-in |
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89 to the PowerVR EGL implementation to implement low-level OpenGL drawing |
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90 surfaces. |
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91 |
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92 \section2 Integrating Other Chipsets |
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93 In this section, we discuss the essential features of the reference |
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94 integration that need to be provided for any other chipset integration. |
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95 |
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96 The QtOpenGL module assumes that a QGLWidget can be represented |
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97 by an \c EGLNativeWindowType value in some underlying window system |
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98 implementation, and that \c{eglSwapBuffers()} is sufficient to copy |
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99 the contents of the native window to the screen when requested. |
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100 |
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101 However, many EGL implementations do not have a pre-existing window system. |
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102 Usually only a single full-screen window is provided, and everything else |
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103 must be simulated some other way. This can be a problem because |
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104 of QtOpenGL's assumptions. We intend to address these assumptions in a |
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105 future version of Qt, but for now, it is the responsibility of the integrator |
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106 to provide a rudimentary window system within the EGL implementation. |
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107 This is the purpose of \c{QWSWSEGL} in the reference integration. |
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108 |
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109 If it isn't possible for the EGL implementation to provide a rudimentary |
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110 window system, then full-screen windows using QGLWidget can be supported, |
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111 but very little else. |
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112 |
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113 The screen driver needs to inherit from QGLScreen and perform the |
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114 following operations in its constructor: |
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115 |
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116 \snippet src/plugins/gfxdrivers/powervr/pvreglscreen/pvreglscreen.cpp 0 |
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117 |
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118 The \c{setSurfaceFunctions()} call supplies an object that takes care |
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119 of converting Qt paint devices such as widgets and pixmaps into |
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120 \c EGLNativeWindowType and \c EGLNativePixmapType values. Here we |
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121 only support native windows. Because OpenGL rendering is direct to |
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122 the screen, we also indicate that client blit is supported. |
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123 |
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124 Next, we override the \c{createSurface()} functions in QGLScreen: |
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125 |
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126 \snippet src/plugins/gfxdrivers/powervr/pvreglscreen/pvreglscreen.cpp 1 |
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127 |
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128 Even if Qt for Embedded Linux is used in single-process mode, it is |
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129 necessary to create both client-side and server-side versions of the |
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130 window surface. In our case, the server-side is just a stub because |
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131 the client side directly renders to the screen. |
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132 |
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133 Note that we only create a \c{PvrEglWindowSurface} if the widget is a |
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134 QGLWidget. All other widgets use the normal raster processing. |
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135 It can be tempting to make \c{createSurface()} create an OpenGL |
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136 window surface for other widget types as well. This has not been |
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137 extensively tested and we do not recommend its use at this time. |
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138 |
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139 The other main piece is the creation of the \c EGLNativeWindowType |
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140 value for the widget. This is done in the \c{createNativeWindow()} |
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141 override: |
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142 |
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143 \snippet src/plugins/gfxdrivers/powervr/pvreglscreen/pvreglscreen.cpp 2 |
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144 |
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145 The details of what needs to be placed in this function will vary |
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146 from chipset to chipset. The simplest is to return the native window |
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147 handle corresponding to the "root" full-screen window: |
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148 |
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149 \code |
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150 *native = rootWindowHandle; |
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151 return true; |
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152 \endcode |
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153 |
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154 The most common value for \c rootWindowHandle is zero, but this may |
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155 not always be the case. Consult the chipset documentation for the |
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156 actual value to use. The important thing is that whatever value is |
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157 returned must be suitable for passing to the \c{eglCreateWindowSurface()} |
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158 function of the chipset's EGL implementation. |
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159 |
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160 In the case of PowerVR, the rudimentary window system in \c{QWSWSEGL} |
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161 provides a \c PvrQwsDrawable object to represent the \c EGLNativeWindowType |
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162 value for the widget. |
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163 |
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164 */ |